Conventionally, an electromotive power assisted bicycle that can run under a pedal effort assisted by electromotive power has been made using a body frame tailored specifically for such a bicycle, and the frame has been further built upon by incorporating an electric motor, a reduction gear, a battery and other components such as a force combining mechanism for adding the electromotive power to the pedal effort. Those components have also been fabricated as dedicated parts adapted to the dedicated body frame.
Among the above components, an example of a type of mechanism that has been suggested as the force combining mechanism includes a unit of dedicated design around a crank shaft such that the pedal effort applied onto the crank shaft and the power transmitted from the electric motor may be output coaxially from the crank shaft. In addition, a chain direct drive system as shown in FIG. 35 has been also suggested. The chain direct drive system includes, mounted on the body frame, an electric motor, a reduction gear for reducing a revolution speed of said electric motor and for outputting a resultant power therefrom and the like, wherein a power sprocket coupled to an output shaft of the reduction gear is, along with a regular sprocket, engaged with a chain for transmitting the pedal effort. At the same time, to ensure a contact angle of the chain over the power sprocket, pulleys are engaged with the chain respectively from the opposite side thereof.
In one method for assembling the battery to the body, an attachment for fixing the battery is mounted to a seat post or a seat tube of the electromotive power assisted bicycle, so that a battery box containing the battery may be installed detachably in said attachment so as to extend from the seat post or the like toward the rear side of the body. According to this attaching method, the attachment is formed into a U-shaped unit comprising a curved portion and a halving portion, in which the curved portion is externally fitted onto the seat post or the like, while a hook of the battery box is clamped in the halving portion, so that the battery box can be fixedly secured to the attachment by tightening a fastener penetrating a bore formed through the halving portion.
The electric motor and the reduction gear housed in a gear box are typically mounted to the body frame in places where they are to be fixed, respectively, as separate components, and covered by a housing or the like. Otherwise, a gear box serving as an electromotive power output unit box containing both of the reduction gear and the electric motor is coupled to the body frame in a place where it is to be fixed.
The above-mentioned gear box comprises, in a typical example, a box having an opening, a cover for closing the opening, and a plurality of bolts for connecting the box and the cover in different positions. FIG. 34 shows a front elevation view of the conventional box viewed from the opening side, wherein a plurality of gears is housed on the inside thereof. The cover is placed over the box shown in FIG. 34, and screws are fastened, or bolts are threaded, over the cover at a plurality of locations to thereby fix the gear. At this time, a shaft end defined in the front side of the gear is held by a bearing provided in an inside of the cover. In FIG. 34, those portions designated by P1, P2, P3 and P4 serve as the locations for the bolts to be attached. Specifically, the bolts are attached along an outer periphery of the box.
However, in the above described prior art, since the electromotive power assisted bicycle is built by providing a specialized body for the electromotive power assisted bicycle and then mounting to said body respective components exclusively tailored therefor, the components can not be adapted to a frame for a regular bicycle, thereby losing versatility. Therefore, those systems according to the prior arts have common problems that they may lead to an increase in cost as well as to a complicated mechanism, resultantly increasing the volume and weight of the electromotive power assisted bicycle. Detailed problems associated with the above-described respective prior arts will now be discussed individually.
In the above-mentioned force combining mechanism according to the prior art, the mechanism of crank coaxial output type needs to employ a structure different from a typical frame around the crank shaft, which may lead to a complex and enlarged profile of the structure around the crank shaft. On the other hand, the prior art force combining mechanism relying on the direct chain drive system shown in FIG. 35 entails a problem that the force combining mechanism is installed exclusively in a location where the chain for transmitting the pedal effort runs therethrough, which is, in actual practice, in a position near the chain (an upper or a lower side thereof) located between the sprocket and a rear wheel. Consequently, the force combining mechanism cannot be installed in a front side of the sprocket. Accordingly, some bicycles still need to have their frames adapted for installing the force combining mechanism, depending on the frame structures thereof. In addition, since in this type of system, such an arrangement as shown in the drawing is essential, in which the pulley is disposed in association with the power sprocket so as to be engaged with the chain in a longitudinal direction serially along a length thereof to ensure the contact angle of the chain over the power sprocket, the degree of flexibility relating to the installation space will be further reduced.
Further, in the mounting system of the battery according to the prior art as described above, since the battery is often placed longitudinally owing to the U-shaped attachment to be used, and in a case that the battery is moved in the vertical direction, a long distance must be provided between the attachment and a saddle, meaning a large space is necessary for attaching and detaching, thus a restriction is imposed on the body frame available for mounting the attachment. Besides, in this mounting system, since the fastener has to be loosened or tightened in response to the detaching or attaching operation of the battery, the attaching and detaching operation takes time, and further disadvantageously, the system entails a problem that a third party may possibly loosen the fastener and steal the battery easily.
The gear box serving as the above electromotive power output unit according to the prior art needs to be adjusted such that its position is precisely relative to the force combining mechanism, so that the electromotive power can be added to the pedal effort correctly, and said gear box also has to be mounted fixedly to the body frame so as not to become displaced with respect thereto. Further, the gear box has to be mounted carefully so as not to interfere with the rigid frame and to thereby offset the gear position. To satisfy these requirements, although in some practices according to the prior art a dedicated body frame has been made, or a special processing has been applied thereto, such attempts have not yet successfully utilized a regular frame manufacturing process. Further, if the electromotive power output unit box is to be mounted without applying any modification to the frame, the electromotive power output unit itself, and attachments used to mount the unit to the frame are apt to be complicated, and furthermore, in such a case the difficulty in positioning is not avoidable. The facts mentioned above are similarly applicable to a case where the electric motor and the reduction gear are separately mounted.
Furthermore, since the conventional gear box shown in FIG. 34 is fastened with screws in the vicinity of the peripheral region thereof, in some gears, the position of a shaft center may be significantly distant from those of the screws. Thus, in such an arrangement having distant screwed positions, if a gear such as a helical gear, for example, that produces a component force in an axial direction of the shaft is used, said component force in the axial direction may produce a deflection in the gear box (especially in the cover) thereby inducing a vibration thereof. Namely, a so-called drumming phenomenon may be induced. Further, since the gear box is deformed and thereby a pitch error may be produced between gears and also a perpendicularity of the gear mounting portion may be distorted, it is more likely to make a sound. Especially, if a flat motor is used, the motor tends to pick up the vibrations from the gear and thereby the motor sound is also magnified.
The present invention has been made in the light of the above facts, and an object thereof is to provide an electromotive power assisted bicycle of a simple mechanism, which enables a bicycle comprising a regular frame to be electrically powered easily by extending the degree of freedom for installation of respective components and also by facilitating a mounting and adjusting operation thereof, thereby solving the above problems.